I want to integrate Card.io's library into my app. Card.IO has a feature where the users enters the CC details manually - I want that to be my custom screen instead of Card.io's screen.
Is that possible?
It is possible. On iOS, you can add card.io as a view:
https://github.com/card-io/card.io-iOS-SDK#integrate-as-a-view
You could, say, use the view-only integration in your own custom view controller with your custom "manual" button that pushes your own custom manual entry view controller.